EFFECTS OF CLIMATIC WARMING ON NORTHERN TREES - TESTING THE FROST DAMAGE HYPOTHESIS WITH METEOROLOGICAL DATA FROM PROVENANCE TRANSFER EXPERIMENTS

According to a hypothesis presented recently the predicted climatic wa rming will cause premature bud burst of trees in Finnish conditions du ring mild spells in mid-winter and heavy frost damage during subsequen t periods of frost. The full stocking and high productivity of norther n Finnish provenances of Picea abies (L.) Karst. grown in central and southern Finland for several decades seemed to conflict with the frost damage hypothesis, because the increase in the annual mean temperatur e involved in the most distant provenance transfers exceeded the predi cted increase in the annual mean temperature in northern Finland. A ca lculation method using air temperature data from provenance transfer e xperiments was developed for testing the frost damage hypothesis. The method was applied with temperature data from Finnish provenence trans fer experiments, assuming for northern Finland both (1) a uniform warm ing scenario of 4.7 degrees C throughout the year and (2) a non-unifor m warming scenario in which the same mean annual temperature increase is applied more to winter than to summer. The results revealed that th e present air temperature conditions in central and southern Finland d o not correspond to those of either of the scenario climates in northe rn Finland; thus the frost damage hypothesis was not falsified. The ca lculation method developed can be used in testing the frost damage hyp othesis in the case of other tree species, locations, and warming scen arios by altering the specifications applied in the method.